1. Field of the Invention
The present invention relates to an optical character reader, and particularly relates to an optical character reader for reading characters written on a sheet of paper while the sheet and an image sensor are moved relative to each other, for example, a hand-held optical character reader for reading characters written on a price label by putting a scanner against the price label by hand.
2. Description of the Prior Art
Conventionally, an optical character reading apparatus has been used to scan an image sensor repeatedly to carry out character recognition with respect to one and the same character so as to improve recognition performance. See, for example, Japanese Pat. Application (unexamined) Publication No. 55-9223.
FIG. 1 (PRIOR ART) shows a prior art optical character reading apparatus. Reading is carried out by placing a scanner 1 above a paper sheet 2 to be read. Characters written on paper 2 are irradiated by light sources 3 and imaged onto image sensor 5 through optical system 4. Image sensor 5 is scanned so that the character image is converted into an electric signal which in turn is converted into a black-and-white picture by a binary encoding circuit 6. A character recognition arrangement 7 recognizes the character and the result of recognition is stored in a storage device 8. According to this prior art device, image sensor 5 may have a size of one character or a size of one line. Character recognition is repeatedly performed by scanning with image sensor 5, and the results of recognition are successively stored in storage device 8. The result of recognition stored in the storage device 8 is then subjected to a decision by a "majority" device 9 to determine a final result 12.
The results of recognition in the optical character reading apparatus may be classified into three cases: a first case in which character recognition has been performed correctly (correct reading); a second case in which character recognition has been performed erroneously (erroneous reading); and a third case in which character recognition has been impossible (reject). The tendency of erroneous reading is different depending on the kind of characters, and the majority processing in the optical character reading apparatus in the prior art has failed to consider this varying tendency of erroneous reading.
Referring to FIGS. 2(a), 2(b) and 2(c), the tendency of erroneous reading in the prior art will be described. FIG. 2(a) shows the tendency of erroneous reading in the case of a character of "T". The character "T" designated by a.sub.1 may be shortened at its lateral bar by binary encoding circuit 6 so that the character "T" designated by al is often transformed into such a form as shown by a.sub.2 or a.sub.3. The forms designated by a.sub.2 and a.sub.3 may be erroneously read as "7" and "1", respectively, by character recognition arrangement 7.
FIG. 2(b) shows the tendency of erroneous reading in the case of a character of "7". If the lateral bar portion of the character "7" designated by b.sub.1 is shortened, the character "7" may be erroneously read as "1". However, the lateral bar is never elongated in accordance with the characteristic of the binary encoding circuit 6, and the character "7" never becomes such a picture as designated by b.sub.3. Accordingly, the character "7" is never erroneously read as "T".
FIG. 2(c) shows the tendency of erroneous reading in the case of a character "1". The lateral bar portion of the character "1" is never elongated, so that the character "1" is never erroneously read as "7" designated by c.sub.2 or "T" designated by c.sub.3.
Thus, the tendency of the erroneous reading depends on the kind of characters.
Since the kind of characters have not been taken into consideration on the decision by majority means in the prior art optical character reading apparatus, there occurs impropriety as shown in the following Table 1.
TABLE 1 ______________________________________ Improper Decision by Majority in the Prior Art Combination of Serial recognition Final No. result result ______________________________________ A 7 7 T 7 B 1 1 T 1 C 1 1 7 1 ______________________________________
Serial number A shows a combination of results of recognition result 7,7, and T when recognition was performed on three figures. According to the conventional decision by majority, the character has been determined to be "7" as the final result. However, the character "7" can never be erroneously read as "T" as shown in FIG. 2(b). On the contrary, in consideration that "T" may be erroneously read as "7", the proper interpretation in serial number A should be that "T" has been correctly read. Similarly, in the case of serial number B, the proper interpretation in consideration of the fact that "1" can never be erroneously read as "T" is that "T" was properly read and "1" was misread. Therefore, in the majority processing in the prior art optical character reading apparatus, the tendency of such erroneous reading depending on the kind of characters has not been taken into consideration, so that the final result has frequently been incorrect.